[ http://issues.apache.org/jira/browse/MODPYTHON-129?page=all ]
Graham Dumpleton reassigned MODPYTHON-129:
------------------------------------------
Assign To: Graham Dumpleton
> HandlerDispatch doesn't treat OK/DECLINED result properly for all phases.
> -------------------------------------------------------------------------
>
> Key: MODPYTHON-129
> URL: http://issues.apache.org/jira/browse/MODPYTHON-129
> Project: mod_python
> Type: Bug
> Components: core
> Versions: 3.2
> Reporter: Graham Dumpleton
> Assignee: Graham Dumpleton
>
> Todays daily bug report, or is it? ;-)
> The Python*Handler documentation says:
> """Multiple handlers can be specified on a single line, in which case they
> will be called sequentially, from left to right. Same handler directives can
> be specified multiple times as well, with the same result - all handlers
> listed will be executed sequentially, from first to last. If any handler in
> the sequence returns a value other than apache.OK, then execution of all
> subsequent handlers is aborted."""
> That is, no matter which phase is being processed, mod_python will stop
> processing them if a value other than OK is returned.
> Problem is that this isn't how Apache itself treats the result from handlers.
> Apache actually implements two different ways for dealing with the result
> from the handlers. Which is used depends on which processing phase is
> occuring. This is all specified by the Apache magic macro code:
> AP_IMPLEMENT_HOOK_RUN_FIRST(int,translate_name,
> (request_rec *r), (r), DECLINED)
> AP_IMPLEMENT_HOOK_RUN_FIRST(int,map_to_storage,
> (request_rec *r), (r), DECLINED)
> AP_IMPLEMENT_HOOK_RUN_FIRST(int,check_user_id,
> (request_rec *r), (r), DECLINED)
> AP_IMPLEMENT_HOOK_RUN_FIRST(int,auth_checker,
> (request_rec *r), (r), DECLINED)
> AP_IMPLEMENT_HOOK_RUN_ALL(int,access_checker,
> (request_rec *r), (r), OK, DECLINED)
> AP_IMPLEMENT_HOOK_RUN_FIRST(int,type_checker,
> (request_rec *r), (r), DECLINED)
> AP_IMPLEMENT_HOOK_RUN_ALL(int,fixups,
> (request_rec *r), (r), OK, DECLINED)
> What this gobblegook expands to are loops which will stop processing handlers
> based on the result.
> For the AP_IMPLEMENT_HOOK_RUN_ALL macro, all handlers in the phase will be
> run unless one returns something other than OK or DECLINED. Returning OK
> means that it did something and it worked okay. Returing DECLINED means that
> it didn't do anything at all. In both these cases, it still goes onto the
> next handler in that phase. After that it will go onto the next phase.
> Returning an error will cause appropriate error response to go back to client
> with any other handlers in the phase, as well as later phases being skipped.
> Returning DONE is much like returning an error but Apache interprets it as
> meaning a complete response was constructed and that it doesn't have to
> generate any response.
> For the AP_IMPLEMENT_HOOK_RUN_FIRST macro, all handlers will be run only if
> they all return DECLINED. In other words, if a handler returns OK it will
> skip the following handlers in that phase and then move onto the next phase.
> Returning an error or DONE is like above.
> In the case of mod_python, what it does doesn't fit into either. It is closer
> to behaving like the AP_IMPLEMENT_HOOK_RUN_ALL macro except that it stops
> processing further handlers in the phase if DECLINED is returned.
> As to what problems this causes, imagine you had registered multiple
> authentication handlers which supported different authentication mechanisms.
> This is the case where AP_IMPLEMENT_HOOK_RUN_FIRST macro is used. The idea
> is that each authentication handler would check the value associated with the
> AuthType directive to determine if it should do anything. If it was not the
> AuthType it implements, if it were a C based handler module, it would
> returned DECLINED to indicate it hadn't done anything and that the next
> handler should instead be tried. Each handler would thus be called until one
> handler says that is for me, says the user is valid and returns OK or returns
> an error rejecting it.
> If you wanted to write these multiple authentication handlers in Python you
> can't do it. This is because the way mod_python works, if you return DECLINED
> it would actually skip the remainder of the mod_python declared handlers
> whereas you still want them to be executed. Apache would still execute any
> other C based handlers in the phase though. The only way to get mod_python to
> execute later mod_python handlers in the phase is to return OK, but if you do
> that and it happens to be the last handler in the mod_python list of
> handlers, it will return OK to Apache and Apache will then think a handler
> successfully handled it and not then execute any subsequent C based handlers
> in that phase.
> There are going to be other sorts of problems with phases implemented using
> AP_IMPLEMENT_HOOK_RUN_ALL as well, as a handler that validly returns DECLINED
> to say it didn't do anything will cause mod_python to skip later mod_python
> handlers as well. If it were only C based handlers, that wouldn't be the case.
> In summary, it doesn't work how it probably should.
> Note that the above relates to phases other than content handler. Still have
> to work out what Apache does for content handler phase when there are
> multiple handlers for the phase.
> No one has probably noticed these problems as no one seems to use mod_python
> in a serious way for implementing these other phases, simply using mod_python
> as a jumping off point for content handlers.
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